UV light having a wavelength of 200 nm to 400 nm can have damaging short-term and long-term effects on the eye. For example, absorption of UV light, especially higher wavelength UV light, by the retina is believed to accelerate or cause retinal injuries such as macular degeneration.
In the field of lenses, such as ophthalmic lenses and sunglass lenses, there is a demand for lenses that protect human eyes from UV light. The addition of UV light absorbing compounds (‘UV absorbers’) in lenses to minimise any detrimental effects of UV light by absorbing light in the region of 290 nm to 400 nm is known.
Plastic optical elements, such as lenses and the like, are commonly manufactured from transparent plastic materials, such as polymers based on diethylene glycol bisallylcarbonate monomers, and polycarbonates. Various methods are known for producing UV light absorbing plastic optical elements, including:                (i) Incorporation of a UV absorber into a monomer followed by polymerising the monomer to give the plastic optical element.        (ii) Imbibing plastic optical elements with a UV absorber by dipping a formed plastic optical element in a solution containing a UV absorber so that the UV absorber is imbibed into the optical element.        (iii) Incorporating a UV absorber in a hard coating on a surface of the plastic optical element.        
Commonly used UV absorbers for plastic lenses in particular are benzophenones and benzotriazoles and their derivatives, such as those having the following structures:

A large number of commercially available plastic lenses capable of absorbing UV light are produced according to the imbibition method mentioned above. However, the imbibition results in an extra step in the manufacturing process. Furthermore, it can be difficult to accurately control the amount of UV absorber that is incorporated into a lens using this method. As to the third method mentioned above, limitations on the thickness of hard coatings means that relatively high concentrations of UV absorber are required to provide a UV cutoff above about 380 nm. However, the abrasion resistance of a hard coat is often compromised at such high concentrations.
As a result of the aforementioned difficulties with the second and third methods, the first method has become a conventional method of fabricating plastic lenses with UV protection.
Plastic lenses based on diethylene glycol bisallylcarbonate (CR-39) monomers in particular are in widespread use. However, there have been problems incorporating UV absorbers into CR-39 lenses, principally because the initiators used to polymerise the CR-39 monomers can also react with UV absorbers that are present in the monomer mixture. More particularly, a high concentration of a peroxide initiator such as diisopropyl peroxydicarbonate (also called isopropyl peroxide (IPP)), dicyclohexyl peroxydicarbonate or benzoyl peroxide is needed to polymerise the monomer. The concentration typically used is around 3% by weight. However, these initiators are also oxidizing reagents that can react with the UV absorber, thereby reducing the effective concentration of the initiator which leads to incomplete polymerisation. This results in a variety of lens defects including softness and/or yellowing.
An additional problem associated with the use of UV absorbers in CR-39 lenses in particular is that the lenses produced are often extremely yellowish, resulting in a poor appearance.
There is a need for compositions and methods for manufacturing optical elements, such as lenses, that are capable of absorbing UV light having in the wavelength range of 300 nm up to 380-400 nm without the lens being unacceptably soft or yellow.
Throughout this specification reference may be made to documents for the purpose of describing various aspects of the invention. However, no admission is made that any reference cited in this specification constitutes prior art. In particular, it will be understood that the reference to any document herein does not constitute an admission that any of these documents forms part of the common general knowledge in the art in any country.
Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.